The use of wireless communications in implantable medical devices is well known in the art. Using both inductive and radio frequency communications, data and commands may be transmitted to an implantable medical device and telemetry data may be received from the implantable medical device. In a radio frequency application, the implantable medical device may utilize a relatively small, space-efficient antenna coupled to an internal transceiver to establish a communication link with an antenna of an external device positioned in proximity of the internal antenna.
The effective range and rate of radio frequency communication may depend in part on a degree to which the impedance of the antenna of the external device matches the impedance of the antenna of the internal device. The closer the impedance match, the clearer the signal between the two antennas may be and the greater the rate the communication may be. Beyond the impact of variance in the componentry utilized in wireless communications, the environment in which the implantable medical device operates may have an impact on the perceived impedance of the internal antenna.
For instance, U.S. Pat. No. 7,409,245, Larson et al., discloses a variable antenna matching network for an implantable antenna. Changes in the patient's body position, weight, composition or other factors may change the antenna efficiency and hinder communication. The disclosed circuit may automatically adjust a matching network for an implanted transceiver to dynamically maximize transmission and reception by controlling the selected value of a plurality of capacitors, inductors and resistors.
However, because of the premium placed on making implantable medical devices relatively small, many internal antennas are not tunable. As a result, manufacturers of implantable medical devices have traditionally made a compromise between maximizing wireless communication efficiency and range and keeping the internal volume of the implantable medical device small.